1. Field of the Invention
The present invention relates to a control method for a sheet member conveying apparatus and a control method for a recording apparatus.
2. Related Background Art
In recent years, a decrease in operation sound, as well as improvement in image quality, are desired in a printer. Particularly, in an ink jet recording apparatus having few noise sources at a time of recording, a DC (direct current) motor and a linear encoder are adopted as a driving means to scan a recording head, thereby achieving a low-noise operation. In addition to this, the DC motor and a rotary encoder are being adopted nowadays as a driving means to convey sheets. Although an effect of decreasing a noise can be expected by only adopting the DC motor, highly developed suspension control techniques and machine accuracy are necessary to execute highly accurate conveying.
As a method of suspending or stopping the DC motor, basically, a method of turning off a power supply of the motor when the rotation of a roller reaches a target position and thus suspending the motor by inertia is generally used.
To secure suspension accuracy using the DC motor, it is necessary and indispensable to lower a pre-suspension speed and eliminate pre-suspension disturbance torque, i.e., to stabilize low-speed driving directly before suspension. That is, by turning off the power supply of the motor at a constant and sufficiently slow speed, a settling time being the time from the start to the suspension of rotation of the motor and suspension accuracy of the motor can be stabilized.
In such a structure, a torque change having a large period can be controlled because the disturbance torque can be eliminated by feedback control represented by generally known PID (proportional-integral-derivative) control. However, a torque change represented by a motor cogging period can not be controlled because a frequency of this torque change exceeds a frequency capable of being solved by the feedback control. This problem will be explained with reference to FIGS. 12 to 14.
FIG. 12 shows an ideal state of a driving profile of a general DC (direct current) motor in a case where tracking (or variable-value) control is used as the feedback control. In FIG. 12, the longitudinal axis indicates a control time and the lateral axis indicates a speed, and the DC motor is driven as indicated by a speed profile 001.
The motor is accelerated in an acceleration control area 002, driven at the maximum speed of the speed profile 001 in a constant speed control area 003, and decelerated in a deceleration control area 004, whereby the rotating speed of the motor reaches a directly-before-suspension speed 005 which satisfies demands of suspension accuracy performance and settling time performance directly before the rotated motor reaches a suspension position. Then, a power supply of the motor is turned off when the rotated motor reaches the target suspension position, and the motor suspends or stops by inertia.
FIGS. 13 and 14 schematically show actual operations in a case where the DC motor controlled aiming at the ideal profile as shown in FIG. 12 is influenced by the torque change. In the drawings, an angle xcex1xc2x0 represents a phase angle where the torque of the motor decreases because of the torque change due to the cogging, and it can be understood that an actual motor driving speed slows whenever the motor passes the point of the angle xcex1xc2x0 and rotates.
The difference between FIGS. 13 and 14 is a difference in a remaining driving phase amount until the motor reaches the target suspension position after it finally passed the point of the angle xcex1xc2x0.
In FIG. 13, since the motor instantly reaches the target suspension position after it finally passed the point of the angle xcex1xc2x0, there is no time to compensate speed decrease due to the torque change, whereby a somewhat too low directly-before-suspension speed 025 is given. In this case, a poor effect such as the settling time becoming long occurs.
In FIG. 14, after the motor finally passed the point of the angle xcex1xc2x0, it reaches the target suspension position after a while. Thus, a correction to recover the speed which decreased too much at the point of the angle xcex1xc2x0 is excessively executed by the feedback control, with the result that a too high directly-before-suspension speed 026 is given by reaction. In this case, a poor effect occurs such as the suspension accuracy degrading a little.
As described above, the suspension accuracy performance and the settling time performance are influenced by differences in a relative offset amount between the target suspension position and a motor cogging torque ripple phase angle, whereby there is the problem that such an influence can not be controlled because it far exceeds the frequency capable of being controlled by the feedback control.
Further, a correlation between the profile of the motor cogging torque ripple and the absolute numeric information being position information obtained from the encoder changes easily, if information in an electronic circuit is lost by power on/off, or a conveying roller is moved while power is off. Therefore, there is a problem that, if an origin judging means for correlating a specific phase angle in the profile with a specific value in the absolute numeric information and correctly judging the correlated value as an origin is not provided, the control based on recognition of the profile can not be executed.
An object of the present invention is to provide a sheet member conveying apparatus control method and a recording apparatus control method which are not influenced easily by a torque change, a speed change and the like of a motor when a sheet member such as a recording medium or the like is conveyed.
Another object of the present invention is to provide a control method for a sheet member conveying apparatus which has a conveying roller for conveying a sheet member, a conveying motor for generating a driving force to drive the conveying roller, a driving transmission means for transmitting the driving force of the conveying motor to the conveying roller, and a detecting means for detecting a position and a speed of the conveying roller, the method comprising a period profile detecting step of detecting a periodic speed change or torque change of the conveying roller as a period profile, an origin judging step of judging a specific phase angle in the period profile as an origin, a correlating step of correlating an offset phase angle having a specific offset from the origin with an optimal suspension phase angle on the period profile being a phase angle to suspend the conveying roller, and a phase managing step of controlling the suspension phase angle control so that the suspension phase angle on the period profile at which the conveying roller suspends becomes the optimal suspension phase angle.